1. Field of the Invention
The present invention generally relates to an electric motor structure that is provided with a rotor cooling structure. More specifically, the present invention relates to an electric motor structure with a rotor cooling structure utilized in both a radial gap electric motor in which a stator and a rotor are arranged to face each other in a radial direction with respect to a rotary shaft, and an axial gap electric motor in which a stator and a disk rotor are arranged along a rotary shaft to face each other in an axial direction with respect to the rotary shaft.
2. Background Information
Some conventional electric motors are equipped with a rotor cooling structure in which a rotor of the electric motor is cooled by a coolant. For example, Japanese Laid-Open Patent Publication No. 2003-219607 discloses a rotor cooling structure for a radial gap electric motor. In this publication, a tubular shape stator and a tubular shape rotor are coaxially arranged with respect to a rotary shaft so as to face each other across a radial gap formed between the stator and the rotor. In this publication, a rotor cooling structure is provided for the radial gap electric motor in which a cone-shaped interstitial coolant passage is formed between the rotor and a rotary shaft in an axial direction of the rotary shaft. The interstitial coolant passage is configured such that an external diameter of the interstitial coolant passage increases as it approaches a coolant outlet from a coolant inlet. Thus, the coolant introduced into the interstitial coolant passage flows from the coolant inlet to the coolant outlet to cool the rotor due to the centrifugal force of the rotor.
Moreover, a rotor cooling structure for an axial gap electric motor in which a stator and a disk rotor are arranged along a rotary shaft such that the stator and the rotor face each other across an axial gap formed between the stator and the rotor has also been proposed. In such rotor cooling structure for an axial gap electric motor, the rotor is provided with a recessed cooling surface portion and a coolant is supplied to the cooling surface portion via a communication passageway formed in the rotary shaft. The centrifugal force of the rotor is utilized to make the coolant flow from radially inward direction to radially outward direction along the cooling surface portion, thereby cooling the rotor.
In both conventional rotor cooling structures for the radial gap electric motor and the axial gap electric motor mentioned above, the coolant is forced against the cooling surface of the rotor by the centrifugal force of the rotor such that a liquid film of the coolant having a prescribed thickness flows across the cooling surface. Thus, the rotor can be cooled with a high level of cooling performance.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved electric motor structure. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.